Because the NSA could track even phone numbers only distantly related to a suspected source believed to be involved in terrorism, it’s entirely possible that a member of Congress‘ records were tracked, said Wisconsin Rep. F. James Sensenbrenner Jr., the Republican author of the Patriot Act, and two other congressmen, Republican Rep. Darrell Issa of California and Democratic Rep. Jerrold Nadler of New York.

In a letter to Mr. Cole, the congressmen said that would be a troubling overstep of executive authority on the legislature.

“As applied to all United States citizens, this program likely violates our Fourth Amendment right to privacy and chills our First Amendment right to free association. As applied to Members of Congress, it also raises grave Separation of Powers concerns for the executive branch to interfere with the private communications of the legislative branch without congressional knowledge,” the lawmakers said.

They raised a hypothetical case of a suspected terrorist who called someone, and that person had at some point called a pizza delivery store, which a member of Congress may also have called. At that point, all of those numbers would be part of the National Security Agency’s so-called “corporate store,” which is a separate database available for analysts to query without the requirement that they be tracking a specific terrorism lead.

The Justice Department didn’t immediately respond to an email seeking comment on Wednesday.

Some members of Congress are raising constitutional questions over the NSA program and whether lawmakers themselves have been caught up in the snooping.

At a House Judiciary Committee hearing on Feb. 4, under questioning by Mr. Issa, Mr. Cole acknowledged that the phone metadata — numbers, times and durations of phone calls — of members of Congress are likely swept up in the NSA’s program.

“Probably we do,” the Justice Department’s No. 2 official said. “We’re not allowed to look at any of those, however, unless we make a reasonable, articulable suspicion finding that that number is associated with a terrorist organization. So while they may be in the database, we can’t look at any of those numbers under the court order without violating the court order.”

As it’s been described by officials and in court documents, the NSA program collects phone records from phone companies and stores the data for five years.

If the agency is alerted to a number that the government has an “articulable” suspicion of being involved with terrorism, analysts were able to look at what other numbers have been in contact with the original number, then look at who has been in contact with those first-degree connected numbers, then look at who has been in contact with those second-degree numbers.

The agency called those “hops” — and said it looked three hops out from the original number.

Last month President Obama announced changes to the program, including limiting queries to just two hops from the original number.